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United States Patent |
5,665,794
|
Maxson
,   et al.
|
September 9, 1997
|
Method for controlling cure initiation and curing times of platinum
group metal curing fluorosilicone compositions
Abstract
A method for controlling cure initiation and curing time of a platinum
group metal curable fluorosilicone composition. The method comprises in a
platinum group metal curable fluorosilicone composition comprising a
cross-linker mixture comprising an alkylhydrogensiloxane and a
dialkylhydrogen perfluoroalkylethylsiloxane controlling the weight ratio
of the alkylhydrogensiloxane to dialkylhydrogen
perfluoroalkylethylsiloxane in the mixture within a range of about 0.1:1
to 9:1 to control the cure initiation and curing time of the composition.
Inventors:
|
Maxson; Myron Timothy (Midland, MI);
Miller; Lee Walter (Bay City, MI)
|
Assignee:
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Dow Corning Corporation (Midland, MI)
|
Appl. No.:
|
650386 |
Filed:
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May 20, 1996 |
Current U.S. Class: |
523/209; 523/212; 524/493; 524/789; 528/15 |
Intern'l Class: |
C08K 009/00 |
Field of Search: |
528/15
524/493,789
523/209,212
|
References Cited
U.S. Patent Documents
3159601 | Dec., 1964 | Ashby.
| |
3220972 | Nov., 1965 | Lamoreaux.
| |
3296291 | Jan., 1967 | Chalk et al.
| |
3419593 | Dec., 1968 | Willing.
| |
3455420 | Jul., 1969 | Blanchard.
| |
3516946 | Jun., 1970 | Modic.
| |
3814730 | Jun., 1974 | Karstedt.
| |
3928629 | Dec., 1975 | Chandra et al.
| |
3989667 | Nov., 1976 | Lee et al.
| |
3989668 | Nov., 1976 | Lee et al.
| |
4584361 | Apr., 1986 | Janik et al.
| |
4732931 | Mar., 1988 | Maxson.
| |
4784879 | Nov., 1988 | Lee et al.
| |
4818805 | Apr., 1989 | Ikeno et al.
| |
4857564 | Aug., 1989 | Maxson.
| |
5036117 | Jul., 1991 | Chung et al.
| |
Primary Examiner: Marquis; Melvyn I.
Attorney, Agent or Firm: Boley; William F.
Claims
We claim:
1. A method for controlling cure initiation time and curing time of a
platinum group metal curable fluorosilicone composition, the method
comprising forming a fluorosilicone composition comprising
(A) 100 parts of a fluorine-containing polydiorganosiloxane comprising at
least two alkenyl radicals per molecule, and repeating units described by
formula R.sup.1 R.sup.f SiO and optionally R.sup.1 R.sup.2 SiO, where
R.sup.1 is an alkyl radical comprising from one to about four carbon
atoms, R.sup.2 is an alkenyl radical comprising from two to about 10
carbon atoms, and R.sup.f is a perfluoroalkyethyl radical comprising from
three to about 12 carbon atoms,
(B) 10 to 70 weight parts of a treated reinforcing silica filler,
(C) an amount of a platinum group metal-containing hydrosilation catalyst
sufficient to effect curing of the composition, and
(D) a crosslinker mixture comprising an alkylhydrogensiloxane comprising at
least 3 silicon-bonded hydrogen atoms per molecule with the remaining
bonds of the silicon atoms being to oxygen or alkyl radicals comprising
one to four carbon atoms and a dialkylhydrogen
perfluoroalkylethylsiloxane; controlling the weight ratio of the
alkylhydrogensiloxane to dialkylhydrogen perfluoroalkylethylsiloxane
within a range of about 0.1:1 to 9:1 to control cure initiation time and
curing time; and curing the fluorosilicone composition.
2. A method according to claim 1, where the weight ratio of the
alkylhydrogensiloxane to dialkylhydrogen perfluoroalkylethylsiloxane is
within a range of about 1:3 to 3:1.
3. A method according to claim 1, where the fluorine-containing
polydiorganosiloxane is a polymer described by formula
QSi(OSiR.sup.1 R.sup.2).sub.a (OSiR.sup.1 R.sup.f).sub.b Q;
where each R.sup.1 is an independently selected alkyl radical comprising
from one to about four carbon atoms, each R.sup.2 is an independently
selected alkenyl radical comprising from two to about 10 carbon atoms,
R.sup.f is a perfluoroalkylethyl radical comprising from three to about 12
carbon atoms, each Q is independently selected from a group consisting of
R.sup.1, R.sup.2, and OH, a.gtoreq.0, a/(a+b)=0 to 0.05, and a+b is a
value such that the polymer has a Williams plasticity number within a
range of about 75 mm/100 to 400 mm/100 at 25.degree. C.
4. A method according to claim 3, where R.sup.1 is methyl, R.sup.2 is
vinyl, R.sup.f is 3,3,3 -trifluoropropyl, Q is hydroxy, a/(a+b) is within
a range of about 0.005 to 0.01 and a+b is a value such that the polymer
has a Williams plasticity number within a range of about 200 mm/100 to 400
mm/100 at 25.degree. C.
5. A method according to claim 1, where the fluorosilicone composition
comprises 30 to 50 weight parts of the treated reinforcing silica filler
per 100 weight parts of component (A).
6. A method according to claim 5, where the treated reinforcing silica
filler has a surface area within a range of about 200 m.sup.2 /g to 400
m.sup.2 /g.
7. A method according to claim 1, where the reinforcing silica filler is
treated with 20 to 50 weight percent, based on the weight of the silica
filler, of a treating agent described by formula HO(R.sup.1 R.sup.f
SiO).sub.x H, where R.sup.1 and R.sup.f are as previously described and X
is a value greater than one.
8. A method according to claim 7, where R.sup.1 is methyl R.sup.f is
3,3,3-trifluoropropyl, and x is a value such that the treating agent has a
viscosity of about 100 mPa.s at 25.degree. C.
9. A method according to claim 7, where the reinforcing silica filler is
treated with 30 to 40 weight percent, based on the weight of the
reinforcing silica filler of a treating agent described by formula
HO(R.sup.1 R.sup.f SiO).sub.x H and 1 to 5 weight percent, based on the
weight of the reinforcing silica filler of a treating agent described by
formula HO(R.sup.1 R.sup.2 SiO).sub.y H; where R.sup.1, R.sup.2, R.sup.f,
and x are as previously described and y is a value greater than one.
10. A method according to claim 9, where R.sup.1 is methyl, R.sup.2 is
vinyl, R.sup.f is 3,3,3-trifluoropropyl, x is a value such that the
treating agent has a viscosity of about 100 mPa.s at 25.degree. C., and y
is a value such the treating agent has a viscosity of about 35 mPa.s at
25.degree. C.
11. A method according to claim 1, where the platinum group
metal-containing hydrosilation catalyst is selected from a group
consisting of platinum metal, platinum compounds, and platinum complexes.
12. A method according to claim 11, where the platinum group
metal-containing hydrosilation catalyst comprises a complex of a platinum
compound with a low-molecular weight vinyl-containing organosiloxane.
13. A method according to claim 12, where the catalyst is microencapsulated
in a matrix or coreshell structure.
14. A method according to claim 1, where the catalyst provides the
equivalent of about 3 to 25 ppm of elemental platinum to the method.
15. A method according to claim 1, where the alkylhydrogensiloxane is
described by formula
R.sup.1.sub.3 Si(OSIR.sup.1.sub.2).sub.e (OSiR.sup.1 H).sub.f
OSiR.sup.1.sub.3,
where each R.sup.1 is an independently selected alkyl radical as previously
described, e>0, f=3 to 200, and e+f=3 to 200.
16. A method according to claim 15, where R.sup.1 is methyl, e+f=6 to 20,
and f/(e+f)>0.6.
17. A method according to claim 1, where the alkylhydrogensiloxane is
described by formula
##STR5##
where each R.sup.1 is an independently selected alkyl radical as
previously described, g=0 to 18, h=3 to 20, and g+h=4 to 20.
18. A method according to claim 17, where R.sup.1 is methyl, g=0, and h=4
to 7.
19. A method according to claim 1, where the alkylhydrogensiloxane is
described by formula
Si(OSiR.sup.1.sub.2 H).sub.4,
where each R.sup.1 is an independently selected alkyl radical as previously
described.
20. A method according to claim 19, where R.sup.1 is methyl.
21. A method according to claim 1, where the dialkylhydrogen
perfluoroalkylethylsiloxane is described by formula
##STR6##
where each R.sup.1 is an independently selected alkyl radical as
previously described, each R.sup.f is an independently selected
perfluoroalkylethyl radical as previously described, and n=1 to 12.
22. A method according to claim 21, where R.sup.1 is methyl, R.sup.f is
3,3,3-trifluoropropyl, and n=2 to 3.
23. A method according to claim 22, where the alkylhydrogensiloxane is
described by formula
R.sup.1.sub.3 Si(OSiR.sup.1.sub.2).sub.e (OSiR.sup.1 H).sub.f
OSiR.sup.1.sub.3,
where R.sup.1 is methyl, e+f=6 to 20, and f/(e+f)>0.6.
24. A curable fluorosilicone composition comprising:
(A) 100 weight parts of a fluorine-containing polydiorganosiloxane
comprising at least two alkenyl radicals per molecule and repeating units
described by formula R.sup.1 R.sup.f SiO and optionally R.sup.1 R.sup.2
SiO, where R.sup.1 is an alkyl radical comprising from one to about four
carbon atoms, R.sup.2 is an alkenyl radical comprising from two to about
10 carbon atoms, and R.sup.f is a perfluoroalkylethyl radical comprising
from three to about 12 carbon atoms,
(B) 10 to 70 parts of a treated reinforcing silica filler,
(C) an amount of a platinum group metal-containing hydrosilation catalyst
sufficient to effect curing of the composition, and
(D) 0.5 to 10 weight parts of a cross-linker mixture comprising an
alkylhydrogensiloxane comprising at least 3 silicon-bonded hydrogen atoms
per molecule with the remaining bonds of the silicon atoms being to oxygen
or alkyl radicals comprising one to four carbon atoms and a
dialkylhydrogen perfluoroalkylethylsiloxane at a weight ratio within a
range of about 0.1:1 to 9:1.
25. A curable fluorosilicone composition resulting from the mixing of
components comprising:
(A) 100 weight parts of a fluorine-containing polydiorganosiloxane
comprising at least two alkenyl radicals per molecule and repeating units
described by formula R.sup.1 R.sup.f SiO and optionally R.sup.1 R.sup.2
SiO, where R.sup.1 is an alkyl radical comprising from one to about four
carbon atoms, R.sup.2 is an alkenyl radical comprising from two to about
10 carbon atoms, and R.sup.f is a perfluoroalkyethyl radical comprising
from three to about 12 carbon atoms,
(B) 10 to 70 weight parts of a reinforcing silica filler,
(C) 20 to 50 weight percent based on the weight of the silica reinforcing
filler of a fluorine-containing treating agent described by formula
HO(R.sup.1 R.sup.f SiO).sub.x H, where R.sup.1 and R.sup.f are as
previously described and x is a value greater than one,
(D) 0 to 10 weight percent based on the weight of the silica reinforcing
filler of an alkenyl-containing treating agent described by formula
HO(R.sup.1 R.sup.2 SiO).sub.y H, where R.sup.1 and R.sup.2 are as
previously described and y has a value greater than one,
(E) an amount of a platinum group metal-containing hydrosilation catalyst
sufficient to effect curing of the composition, and
(D) 0.5 to 10 weight parts of a cross-linker mixture comprising an
alkylhydrogensiloxane comprising at least 3 silicon-bonded hydrogen atoms
per molecule with the remaining bonds of the silicon atoms being to oxygen
or alkyl radicals comprising one to four carbon atoms and a
dialkylhydrogen perfluoroalkylethylsiloxane at a weight ratio within a
range of about 0.1:1 to 9:1.
26. A method according to claim 1, where the alkylhydrogensiloxane is
described by formula
(R.sup.1.sub.3 SiO.sub.1/2).sub.i (R.sup.1.sub.2 SiO.sub.2/2).sub.j
(R.sup.1 HSiO.sub.2/2).sub.k (R.sup.1 SiO.sub.3/2).sub.m,
where each R.sup.1 is an independently selected alkyl radical as previously
described, i=6 to 20, j=15 to 45, k=30 to 80, and m=2 to 6.
27. A method according to claim 26 where R.sup.1 is methyl.
Description
BACKGROUND OF INVENTION
The present invention is a method for controlling cure initiation time and
curing time of a platinum group metal curable fluorosilicone composition.
The method comprises in a platinum group metal curable fluorosilicone
composition comprising a cross-linker mixture comprising an
alkylhydrogensiloxane and a dialkylhydrogen perfluoroalkylethylsiloxane
controlling the weight ratio of the alkylhydrogensiloxane to
dialkylhydrogen perfluoroalkylethylsiloxane in the mixture within a range
of about 0.1:1 to 9:1 to control the cure initiation and curing time of
the composition.
It is known in the art that fluorosilicone elastomers maintain desirable
physical properties over a wide temperature range and have good resistance
to hydrocarbons such as gasoline and engine oil. Therefore, fluorosilicone
elastomers are useful as gasket and seals in a wide variety of
applications. The ability to mold such gaskets, seals, and other articles
from fluorosilicone compositions accurately and quickly is necessary for
cost competitiveness of such moldings. For moldings prepared from
fluorosilicone compositions to be cost competitive it is necessary that
the compositions have a cure initiation time sufficient to allow complete
filling of a mold cavity and then for the composition to cure rapidly
allowing for a rapid cycle time for the molding operation.
It is also known that fluorosilicone compositions can be cured by an
addition-type reaction using a platinum catalyst and an
alkylhydrogensiloxane as a cross-linker. Generally, the use of an
alkylhydrogensiloxane as cross-linker in fluorosilicone compositions
provides for a composition that has a relatively long cure initiation and
cure time. Therefore, although such compositions can provide for a
complete filling of a mold cavity prior to cure initiation, the molding
cycle time is slow.
Ikeno et al., U.S. Pat. No. 4,818,805, discuss the issue relating to the
relative slow cure initiation and curing time of fluorosilicone
compositions using an alkylhydrogensiloxane as cross-linker. Ikeno et al.
describe the use of an unique siloxane cross-linker containing
silicon-bonded hydrogen atoms, fluorine substituted organic substituents
bonded to silicon, and a divalent organic group with both valencies bonded
to separate silicon atoms for curing of fluorosilicone compositions. The
siloxane cross-linker described by Ikeno et al. is report to provide for a
quick cure initiation and fast curing of fluorosilicone compositions.
Maxson, U.S. Pat. No. 4,732,931 and U.S. Pat. No. 4,857,564 describes
platinum curing fluorosilicone compositions comprising a dialkylhydrogen
trifluoropropylsiloxane cross-linker having repeating units described by
formula
##STR1##
where Prf represents a 3,3,3-trifluoropropyl group. The compositions
described by Maxson are known to have fast cure initiation and curing
times. The disadvantage of these fast cure initiation times is that large
or complex molds may not have time to fill completely before curing is
initiated. This results in a large number of device rejects.
The present invention provides a method where the cure initiation and cure
time of a platinum curing fluorosilicone composition can be tailored over
a significant range to allow for accurate and rapid molding of
fluorosilicone devices. The method comprises in a cross-linker mixture
controlling the weight ratio of an alkylhydrogensiloxane to
dialkylhydrogen perfluoroalkylethylsiloxane within a range of about 0.1:1
to 9:1. An important aspect of this invention is the discovery that the
ratio of the cross-linkers can be varied within the described range while
maintaining acceptable physical properties of the cured fluorosilicone
elastomer.
SUMMARY OF INVENTION
A method for controlling cure initiation and curing time of a platinum
group metal curable fluorosilicone composition. The method comprises in a
platinum group metal curable fluorosilicone composition comprising a
cross-linker mixture comprising an alkylhydrogensiloxane and a
dialkylhydrogen perfluoroalkylethylsiloxane controlling the weight ratio
of the alkylhydrogensiloxane to dialkylhydrogen
perfluoroalkylethylsiloxane in the mixture within a range of about 0.1:1
to 9:1 to control the cure initiation and curing time of the composition.
DESCRIPTION OF INVENTION
The present invention is a method for controlling cure initiation and
curing time of a platinum group metal curable fluorosilicone composition.
The method comprises in a platinum group metal curable fluorosilicone
composition comprising a cross-linker mixture comprising an
alkylhydrogensiloxane and a dialkylhydrogen perfluoroalkylethylsiloxane
controlling the weight ratio of the alkylhydrogensiloxane to
dialkylhydrogen perfluoroalkylethylsiloxane in the mixture within a range
of about 0.1:1 to 9:1 to control the cure initiation and curing time of
the composition. In a preferred embodiment of the present method the
fluorosilicone composition comprises:
(A) 100 weight parts of a fluorine-containing polydiorganosiloxane
comprising at least two alkenyl radicals per molecule and repeating units
described by formula R.sup.1 R.sup.f SiO and optionally R.sup.1 R.sup.2
SiO, where R.sup.1 is an alkyl radical comprising from one to about four
carbon atoms, R.sup.2 is an alkenyl radical comprising from two to about
10 carbon atoms, and R.sup.f is a perfluoroalkylethyl radical comprising
from three to about 12 carbon atoms,
(B) 10 to 70 weight parts of a treated reinforcing silica filler,
(C) an amount of a platinum group metal-containing hydrosilation catalyst
sufficient to effect curing of the composition, and
(D) 0.5 to 10 weight parts of a cross-linker mixture comprising an
alkylhydrogensiloxane and a dialkylhydrogen perfluoroalkylethylsiloxane at
a weight ratio within a range of about 0.1:1 to 9:1.
The curable fluorosilicone compositions of the present invention require
the presence of a fluorine-containing polydiorganosiloxane comprising at
least two alkenyl radicals per molecule and repeating units described by
formula R.sup.1 R.sup.f SiO and optionally R.sup.1 R.sup.2 SiO, where
R.sup.1, R.sup.2 and R.sup.f are as previously described. The
fluorine-containing polydiorganosiloxane can be a polymer or mixture of
polymers described by formula
QSi(OSiR.sup.1 R.sup.2).sub.a (OSiR.sup.1 R.sup.f).sub.b Q,(1)
where R.sup.1, R.sup.2, and R.sup.f are as previously described, each Q is
independently selected from a group consisting of R.sup.1, R.sup.2 and OH,
a.gtoreq.0, a/(a+b)=0 to 0.05, and a+b is a value such that the polymer
has a Williams plasticity number within a range of about 75 mm/100 to 400
mm/100 at 25.degree. C. as determined by ASTM D926. The substituent
R.sup.1 of the fluorine-containing polydiorganosiloxane can be, for
example, methyl, ethyl, propyl, and tert-butyl. Preferred is where R.sup.1
is methyl. The substituent R.sup.2 can be, for example, vinyl, allyl,
pentenyl, hexenyl. and decenyl. Preferred is where R.sup.2 is vinyl. The
substituent R.sup.f is a perfluoroalkylethyl radical where the silicon
atom is separated from the perfluoroalkyl radical by two non-fluorinated
carbon atoms. The perfluoroalkyl portion of R.sup.f can contain from one
to about 10 carbon atoms. R.sup.f can be, for example, perfluoromethyl,
perfluoroethyl, perfluorobutyl and perfluorooctyl. Preferred is when
R.sup.f is 3,3,3-trifluoropropyl. In formula (1) it is preferred that Q be
selected from a group consisting of methyl, vinyl, and hydroxy. In formula
(1) it is most preferred that Q be hydroxy. In formula (1) subscript a can
be a value of zero or greater. Preferred is when subscript a is a value
such that a/(a+b) is within a range of about 0.002 to 0.05. More preferred
is when subscript a is a value such that a/(a+b) is within a range of
about 0.005 to 0.01.
In formula (1) it is preferred that a+b be a value such that the polymer or
mixture of polymers has a Williams plasticity number within a range of
about 100 mm/100 to 400 mm/100 at 25.degree. C. More preferred is when the
Williams plasticity number is within a range of about 200 mm/100 to 400
mm/100 at 25.degree. C. In a preferred fluorine-containing
polydiorganosiloxane for use in compositions of the present invention
R.sup.1 is methyl, R.sup.f is 3,3,3-trifluoropropyl, Q is a hydroxy
radical, subscript a is a value such that a/(a+b) is about 0.01, and a+b
is a value such that the fluorine-containing polydiorganosiloxane has a
Williams plasticity number within a range of about 200 mm/100 to 300
mm/100 at 25.degree. C.
The platinum curable fluorosilicone compositions of the present method
require the presence of 10 to 70 weight parts of a treated reinforcing
silica filler per 100 weight parts of the fluorine-containing
polydiorganosiloxane (component A). The treated reinforcing silica filler
improves the physical strength of the cured fluorosilicone elastomers
prepared from the composition. Preferred is when the present composition
comprises about 30 to 50 weight parts of the treated reinforcing silica
filler per 100 weight parts of component (A). The reinforcing silica
filler can be of the fumed or precipitated type and should have a BET
surface area of at least about 50 m.sup.2 /g. Preferred is when the
reinforcing silica filler is of the fumed type. Preferred is when the
reinforcing silica filler has a surface area greater than about 100
m.sup.2 /g. Even more preferred is when the reinforcing silica filler has
a surface area within a range of about 200 m.sup.2 /g to 400 m.sup.2 /g.
The reinforcing silica filler of the present composition is treated with
one or more low molecular weight organosilicon compounds to prevent a
phenomenon referred to as "creping" or "crepe harding". These silica
treating agents reduce the interaction between the fluorine-containing
polydiorganosiloxane and the reinforcing silica filler that causes the
curable composition to undergo an increase in viscosity during blending
and storage of the composition, to the extent that the composition is
difficult to process using conventional techniques and equipment. Those
skilled in the art will recognize that the treating agent or agents may
also serve to improve physical properties of the cured fluorosilicone
elastomers prepared from the present compositions.
Suitable silica treating agents are well known in the art and include, for
example, liquid silanol-containing organosilicon compounds and
organosilicon compounds such as organodisilazanes that can be hydrolyzed
to form these compounds under the conditions used to treat the silica.
Hydrolyzable precursors of silanol-containing silica treating agents
include, for example, cyclic polydiorganosiloxanes, silazanes, and linear
polydiorganosiloxanes containing alkoxy or other readily hydrolyzable
groups. Preferred silica treating agents are selected from a group
described by formula
HO(R.sup.1 R.sup.f SiO).sub.x H (2)
and
HO(R.sup.1 R.sup.2 SiO).sub.y H (3)
where R.sup.1, R.sup.2, and R.sup.f are as previously described, x is a
value greater than one, and y is a value greater than one. A preferred
treating agent described by formula (2) is where R.sup.1 is methyl,
R.sup.f is 3,3,3-trifluoropropyl, and x is a value such that the treating
agent has a viscosity of about 100 mPa.s at 25.degree. C. A preferred
treating agent described by formula (3) is where R.sup.1 is methyl,
R.sup.2 is vinyl, and y is a value such that the treating agent has a
viscosity of about 35 mPa.s at 25.degree. C. In the present compositions
it is preferred that the reinforcing silica filler be treated with 20 to
50 weight percent, based on the weight of the silica filler, of the
treating agent described by formula (2). More preferred is when the
reinforcing silica filler is treated with about 30 to 40 weight percent,
based on the weight of the silica, of the treating agent described by
formula (2). In the present compositions the reinforcing silica filler can
be treated with 0 to 10 weight percent, based on the weight of the filler,
of a treating agent described by formula (3). Preferred is when the
reinforcing silica filler is treated with about 1 to 5 weight percent,
based on the weight of the silica, of a treating agent described by
formula (3). In the present compositions it is most preferred that the
reinforcing silica filler be treated with 30 to 40 weight percent of the
treating agent described by formula (2) and 1 to 5 weight percent of the
treating agent described by formula (3), based on the weight of the
silica. The reinforcing silica can be pretreated with one or more treating
agent prior to addition to the composition or may be treated in situ.
The curable fluorosilicone compositions of the present method require the
presences of a catalytic amount of a platinum group metal-containing
hydrosilation catalyst. The platinum group metal-containing catalyst can
be any of those known to catalyze the reaction of silicon-bonded hydrogen
atoms with silicon-bond alkenyl groups. By "platinum group metal" it is
meant ruthenium, rhodium, palladium, osmium, iridium, and platinum.
Examples of useful platinum group metal-containing catalysts can be found
in Lee et al., U.S. Pat. No. 3,989,668; Chang et al., U.S. Pat. No.
5,036,117; Ashby, U.S. Pat. No. 3,159,601; Lamoreaux, U.S. Pat. No.
3,220,972; Chalk et al., U.S. Pat. No. 3,296,291; Modic, U.S. Pat. No.
3,516,946; Karstedt, U.S. Pat. No. 3,814,730; and Chandra et al., U.S.
Pat. No. 3,928,629 all of which are hereby incorporated by reference to
show useful platinum group metal-containing catalyst and methods for their
preparation.
The preferred platinum group metal for use as a catalyst to effect cure of
the present compositions by hydrosilation is platinum. Therefore, a
preferred catalyst for curing the present compositions is selected from a
group consisting of platinum metal, platinum compounds, and platinum
complexes. Platinum compounds such as chloroplatinic acid, chloroplatinic
acid hexahydrate, and platinum dichloride and particularly complexes of
such compounds with low-molecular weight vinyl-containing organosiloxanes
are one group of preferred catalysts. These complexes are described in
Willing, U.S. Pat. No. 3,419,593, which is hereby incorporated by
reference for its teaching of such complexes. Complexes of platinum
compounds with low-molecular weight organosiloxanes where the silicon
bonded hydrocarbon radicals are vinyl and either methyl or
3,3,3-trifluoropropyl are particularly preferred because of their ability
to catalyze a rapid curing of the present compositions at temperatures
greater than about 70.degree. C.
The most preferred catalysts for use in the present compositions are those
where the platinum group metal-containing catalyst, particularly when the
platinum group metal is platinum, is microencapsulated in a matrix or
coreshell type structure. The platinum group metal-containing catalyst can
be encapsulated, for example, in a dimethylphenylsiloxane resin.
Microencapsulated platinum group metal-containing catalyst along with
methods for their preparation are described in Lee et al., U.S. Pat.
4,784,879, which is incorporated by reference for its teaching of such
catalysts useful in the present compositions.
The platinum group metal-containing catalyst may be added to the present
compositions in an amount equivalent to as little as 0.001 part by weight
of elemental platinum group metal per one millions parts (ppm) of the
composition. Preferably, the concentration of platinum group metal in the
composition is that providing the equivalent of a least 1 ppm of elemental
platinum group metal in the composition. A catalyst concentration
providing the equivalent of about 3 to 25 ppm of elemental platinum group
metal in the composition is preferred.
The present invention is a method for controlling cure initiation and
curing time of a platinum group metal curable fluorosilicone composition.
Therefore, the compositions prepared by the method can be tailored to
provide an initiation time sufficient to allow a mold to be completely
fill with the composition before curing restricts flow in the mold and to
provide for a rapid cure time thereafter to allow for a rapid cycle time
for the molding process. The present inventors have unexpectly found that
cure initiation time and curing time can be controlled by use of a
cross-linker mixture comprising an alkylhydrogensiloxane and a
dialkylhydrogen perfluoroalkylethylsiloxane where the ratio of the
alkylhydrogensiloxane to dialkylhydrogen perfluoroalkylethylsiloxane is
controlled within a range of about 0.1:1 to 9:1. Generally, increasing the
amount of alkylhydrogensiloxane in the mixture increases cure initiation
time and increases cure time. Increasing the amount of dialkylhydrogen
perfluoroalkylethylsiloxane in the process decreases cure initiation time
and decreases cure time.
The alkylhydrogensiloxane present in the cross-linker mixture is limited
only in that it must have at least three silicon-bonded hydrogen atoms per
molecule, with the remaining bonds of the silicon atoms being to oxygen or
alkyl radicals comprising one to four carbon atoms. Non-limiting examples
of useful alkylhydrogensiloxanes include those described by formulas:
R.sup.1.sub.3 Si(OSiR.sup.1.sub.2).sub.e (OSiR.sup.1 H).sub.f
OSiR.sup.1.sub.3, (4)
where each R.sup.1 is an independently selected alkyl radical as previously
described, e.gtoreq.0, f=3 to 200, and e+f=3 to 200;
##STR2##
where each R.sup.1 is an independently selected alkyl radical as
previously described, g=0 to 18, h=3 to 20, and g+h=4 to 20;
Si(OSiR.sup.1.sub.2 H).sub.4 (6)
where R.sup.1 is as previously described; and
(R.sup.1.sub.3 SiO.sub.1/2).sub.i (R.sup.1.sub.2 SiO.sub.2/2).sub.j
(R.sup.1 HSiO.sub.2/2).sub.k (R.sup.1 SiO.sub.3/2) (7)
where R.sup.1 is as previously described, i=6 to 20, j=15-45, k=30 to 80,
m=2 to 6.
In formulas (4), (5), (6), and (7) it is preferred that R.sup.1 be methyl.
In formula (4) it is preferred that f/(e+f)>0.6 and even more preferred is
when e+f=6 to 20 and f/(e+f)>0.6. In formula (5) it is preferred that g=0
and h=4 to 7.
The dialkylhydrogen perfluoroalkylethylsiloxane present in the cross-linker
mixture is described by formula
##STR3##
where R.sup.1 and R.sup.f are as previously described and n=l to 12. In
formula (8) it is preferred that R.sup.1 be methyl and R.sup.f be
3,3,3-trifluoropropyl. In formula (8) it is preferred that n=l to 3. More
preferred in formula (8) is when x=2 to 3.
In the cross-linker mixture, the weight ratio of the alkylhydrogensiloxane
(cross-linker A) to dialkylhydrogen perfluoroalkylethylsiloxane
(cross-linker B) can be controlled within a range of about 0.1:1 to 9:1 as
a means of controlling the cure initiation and curing time of the present
compositions. Preferred is when the weight ratio of cross-linker A to
cross-linker B is within a range of about 1:3 to 3:1.
The molar ratio of silicon-bonded hydrogen atoms provided to the
composition by the cross-linker mixture to total concentration of
silicon-bonded alkenyl radicals present in the composition is important
with respect to the properties of the cured fluorosilicone elastomers
formed from the composition. The optimum ratio for the present composition
will be determined at least in part by the concentration of silicon-bonded
alkenyl radicals present in the composition and the composition of the
cross-linker mixture. Generally a useful molar ratio of silicon-bonded
hydrogen atoms to silicon-bonded alkenyl radicals is within a range of
about 1:1 to 5:1.
Preferred embodiments of the present invention use a microencapsulated
platinum containing catalyst and may be formulated as one-part curable
compositions. However, to extend the shelf-life of such compositions and
those compositions using non-encapsulated platinum group metal-containing
catalysts it may be useful to add a catalyst inhibitor to the composition.
Such platinum group metal-containing catalyst inhibitors are known in the
art and include acetylenic compounds as disclosed in Kookootsedes et al.,
U.S. Pat. No. 3,445,420. Acetylenic alcohols such as 2-methyl-3-butyn-2-ol
and 1-ethynyl-1-cyclohexanol are preferred inhibitors that suppress the
activity of a platinum group metal-containing catalyst at ambient
temperature while allowing curing to proceed rapidly at elevated
temperatures.
Other platinum group metal-containing inhibitors that may be used in the
present compositions include those described in Chung et al., U.S. Pat.
No. 5,036,117; Janik, U.S. Pat. No. 4,584,361; and Lee et al., U.S. Pat.
No. 3,989,667.
The amount of platinum group metal-containing catalyst inhibitor required
is that needed to produce the desired shelf-life and/or pot-life and yet
not extend the cure time of the composition to an impractical level. The
amount of inhibitor required will vary widely and will depend upon the
particular inhibitor that is used, the nature and concentration of the
platinum group metal-containing catalyst, and the composition of the
cross-linker mixture. Inhibitor added in amounts as small as one mole of
inhibitor per mole of platinum group metal will in some instances cause a
satisfactory inhibition of the catalyst. In other cases, as much as 500
moles of inhibitor per mole of platinum group metal may be needed to
achieve the desired combination of pot life and cure time. When the
catalyst is a microencapsulated platinum group metal-containing catalyst,
low concentrations of inhibitors, particularly the acetylenic alcohols,
may accelerate the curing reaction at elevated temperatures. This
acceleration of curing can be determined by standard methods and the
concentration of the inhibitor adjusted appropriately.
To provide for improved storage stability of the present compositions, the
compositions may be packaged in two parts with the platinum group
metal-containing catalyst in one part and the cross-linker mixture in the
other part.
Compositions prepared by the present method can have added to them optional
ingredients such as heat stabilizers, pigments, flame-retardants, mold
release agents, chain extenders, and extending fillers such as ground
quartz.
A preferred method for preparing the present curable compositions is to mix
the reinforcing silica filler with the fluorine-containing
polydiorganosiloxane to form a homogeneous blend and then add the silica
treating agents or agents as described herein. The mixing operation can be
conducted under relatively high shear using, for example, a dough-type
mixer. When the silica treating agents are of the hydrolyzable type it may
be necessary to add appropriate amounts of water to the composition to
facilitate the hydrolysis. The mixing and reinforcing silica treating
operation can require anywhere from about 15 minutes to 2 hours, depending
upon such factors as the amount of material being processed, the viscosity
of the material, and the shear rate of the mixer. It is preferred that the
latter part of the mixing operation be conducted at a temperature within a
range of about 100.degree. C. to 250.degree. C. under reduced pressure to
remove volatiles from the composition.
After the above described composition is cooled to about ambient
temperature the other components of the composition including the platinum
group metal-containing catalyst, the cross-linker mixture, and any
optional ingredients may be added.
The following examples are provided to illustrate the present invention.
These examples are not intended to limit the scope of the claims herein.
In the examples Me, Vi, and Rf represent methyl, vinyl, and
3,3,3-trifluoropropyl respectively and the Williams plasticity is that
determined at 25.degree. C. by ASTM D926.
Examples. A curable fluorosilicone composition as described in Table 1 was
prepared by the method described above. The weight ratio of the
alkylhydrogensiloxane (cross-linker A) to dialkylhydrogen
perfluoroalkylethylsiloxane (cross-linker B) was varied as described in
Table 2 and the cure initiation time, cure rate, and physical properties
of the cured fluorosilicone elastomer determined. The cure initiation time
is defined herein as the scorch time in minutes as determined by rheometer
testing at 177.degree. C. with a 3 degree arc and a sweep time of 12
minutes. The cure rate is expressed herein as the T.sub.50 and T.sub.90
times in minutes as determined by rheometry as described above, where the
T.sub.50 and T.sub.90 times are the times required to reach 50% and 90%
torque respectively. Cured fluorosilicone elastomers suitable for physical
properties testing were prepared from the described compositions by curing
in a mold for 10 minutes at 171.degree. C. and post-curing for 4 hours at
200.degree. C. Typical physical properties of these cured samples were
determined by the following test methods: Shore A durometer (Duro.) ASTM
2240, tear (die B) ASTM 625, compression set ASTM 395, and tensile,
elongation, and modulus (100%) by ASTM 412. The results of the physical
properties testing are provided in Table 2.
TABLE 1
______________________________________
Formulation of Tested Compositions
No. Parts (Wt.)
Component Description
______________________________________
1 100 Methyl(3,3,3-trifluoropropyl)hydroxysiloxy
terminated methyl(3,3,3-
trifluoropropyl)(methylvinyl)polysiloxane
comprising 1 mole percent of MeViSiO units and
having a Williams plasticity of 300 mm/100
2 36.3 Fumed silica, BET surface area of 400 m.sup.2 /g
3 0.8 Fumed silica, BET surface area of 200 m.sup.2 /g
4 13.3 Methyl(3,3,3-trifluoropropyl)hydroxysiloxy
terminated methyl(3,3,3-trifluoropropyl)polysilox-
ane having a viscosity of 100 mPa .multidot. s at
25.degree. C.
5 1.0 Methylvinylhydroxysiloxy terminated
methylvinylpolysiloxane having a viscosity of 35
mPa .multidot. s at 25.degree. C.
6 3.0 Encapsulated platinum containing catalyst com-
prising 4 weight percent platinum, where the
catalyst is prepared by spray drying a solvent mix-
ture comprising a neutralized complex of
chloroplatinic acid hexahydrate with sym-
tetramethyldivinylsiloxane and a dimethylphenyl-
siloxane resin
7 0.5 1-Ethynyl-1-cyclohexanol
8 1.6 MeViSi(N(Me)C(O)Me).sub.2
9 13.1 ground quarts, 5-10 micron particle size
10 3.1 blue pigment
11 4.0 Cross-linker mixture as described in Table
______________________________________
2
TABLE 2
______________________________________
Effect of Cross-linker Mixture on cure and Physical Properties
Cross-linker*
Parts Cross-linker
______________________________________
A1 4 3 2 1 0 0 0
A2 0 0 0 0 0 1 4
B 0 1 2 3 4 3 0
Cure Properties
Scorch Time (Min.)
2.3 2.1 2.0 1.4 0.8 1.3 2.2
T.sub.50 (Min.)
4.4 3.2 3.0 2.7 2.2 2.9 3.6
T.sub.90 (Min.)
9.5 8.0 7.0 6.0 4.3 7.3 9.7
Physical Properties
Duro. (Shore A)
72 70 72 70 74 74 73
Tensile, MPa
6.2 6.6 6.7 6.7 6.8 7.1 5.9
Tear (Die B), kN/m
21.2 21.5 21.5 21.0 20.8 20.1 17.5
Elongation, %
214 231 219 210 169 192 165
Modulus (100%), MPa
3.5 3.4 3.6 3.7 4.2 4.3 4.1
Compression Set, %
59 43 43 45 -- 45 56
______________________________________
*Al = Me.sub.3 Si(OSiMe.sub.2).sub.3 (OSiMeH).sub.5 OSiMe.sub.3
*A2 = (Me.sub.3 SiO.sub.1/2).sub.12.7 (Me.sub.2 SiO).sub.29.1
(MeHSiO).sub.54.6 (MeSiO.sub.3/2).sub.3.6
##STR4##
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